High-frequency gravity waves and homogeneous ice nucleation in tropical tropopause layer cirrus

2016 ◽  
Vol 43 (12) ◽  
pp. 6629-6635 ◽  
Author(s):  
Eric J. Jensen ◽  
Rei Ueyama ◽  
Leonhard Pfister ◽  
Theopaul V. Bui ◽  
M. Joan Alexander ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Ice Nucleation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

scholarly journals Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

2013 ◽  
Vol 13 (19) ◽  
pp. 9801-9818 ◽  
Author(s):  
P. Spichtinger ◽  
M. Krämer
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Full Range ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Homogeneous Freezing

Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s−1) and faster (> 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

scholarly journals Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

2012 ◽  
Vol 12 (10) ◽  
pp. 28109-28153 ◽  
Author(s):  
P. Spichtinger ◽  
M. Krämer
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Full Range ◽  
Ice Nucleation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Homogeneous Freezing

Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results of the scenarios are mixed for both heterogeneous/homogeneous and pure homogeneous ice formation occurring in very slow (<1 cm s−1) and faster (>1 cm s−1) large-scale updraughts. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

scholarly journals Cold trap dehydration in the Tropical Tropopause Layer characterized by SOWER chilled-mirror hygrometer network data in the Tropical Pacific

2012 ◽  
Vol 12 (9) ◽  
pp. 25833-25885 ◽  
Author(s):  
F. Hasebe ◽  
Y. Inai ◽  
M. Shiotani ◽  
M. Fujiwara ◽  
H. Vömel ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Tropical Pacific ◽  
Cold Trap ◽  
Mixing Ratio ◽  
Back Trajectories ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Scatter Plots ◽  
Cold Point ◽  
The Tropical Pacific

Abstract. A network of balloon-born radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since late 1990s in the Tropical Pacific trying to capture the progress of dehydration for the air parcels advected horizontally in the Tropical Tropopause Layer (TTL). The analyses of this dataset are made on isentropes taking advantage of the conservative properties of tracers in adiabatic motion. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in the relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Further observational evidence is needed to confirm the credibility of such high values of RHice. The progress of TTL dehydration is reflected in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. The supersaturation exceeding the critical value of the homogeneous ice nucleation (OMR > 1.6 × SMRmin) is frequently observed on 360 and 365 K surfaces indicating that the cold trap dehydration is under progress in the TTL. The near correspondence between the two (OMR ~ SMRmin) on 380 K on the other hand implies that this surface is not significantly cold for the advected air parcels to be dehydrated. Above 380 K, the cold trap dehydration would scarcely function while some moistening in turn occurs before the air parcels reach the lowermost stratosphere at around 400 K where OMR is generally smaller than SMRmin.

scholarly journals Ice nucleation and dehydration in the Tropical Tropopause Layer

2013 ◽  
Vol 110 (6) ◽  
pp. 2041-2046 ◽  
Author(s):  
E. J. Jensen ◽  
G. Diskin ◽  
R. P. Lawson ◽  
S. Lance ◽  
T. P. Bui ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2016 ◽  
Vol 16 (1) ◽  
pp. 35-46 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved.With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, a low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INCs.

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2015 ◽  
Vol 15 (6) ◽  
pp. 8771-8799 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INC.

scholarly journals Cold trap dehydration in the Tropical Tropopause Layer characterised by SOWER chilled-mirror hygrometer network data in the Tropical Pacific

2013 ◽  
Vol 13 (8) ◽  
pp. 4393-4411 ◽  
Author(s):  
F. Hasebe ◽  
Y. Inai ◽  
M. Shiotani ◽  
M. Fujiwara ◽  
H. Vömel ◽  
...  
Keyword(s):  
Ice Nucleation ◽  
Tropical Pacific ◽  
Cold Trap ◽  
Mixing Ratio ◽  
Back Trajectories ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Scatter Plots ◽  
Cold Point ◽  
The Tropical Pacific

Abstract. A network of balloon-borne radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since the late 1990s in the Tropical Pacific to capture the evolution of dehydration of air parcels advected quasi-horizontally in the Tropical Tropopause Layer (TTL). The analysis of this dataset is made on isentropes taking advantage of the conservative properties of tracers moving adiabatically. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Although further observational evidence is needed to confirm the credibility of such high values of RHice, the evolution of TTL dehydration is evident from the data in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. Supersaturation exceeding the critical value of homogeneous ice nucleation (OMR > 1.6 × SMRmin) is frequently observed on the 360 and 365 K surfaces indicating that cold trap dehydration is in progress in the TTL. The near correspondence between the two (OMR ~ SMRmin) at 380 K on the other hand implies that this surface is not sufficiently cold for the advected air parcels to be dehydrated. Above 380 K, cold trap dehydration would scarcely function while some moistening occurs before the air parcels reach the lowermost stratosphere at around 400 K where OMR is generally smaller than SMRmin.

scholarly journals Impact of gravity waves on the motion and distribution of atmospheric ice particles

2018 ◽  
Vol 18 (14) ◽  
pp. 10799-10823 ◽  
Author(s):  
Aurélien Podglajen ◽  
Riwal Plougonven ◽  
Albert Hertzog ◽  
Eric Jensen
Keyword(s):  
Relative Humidity ◽  
Gravity Waves ◽  
Ice Crystals ◽  
Lapse Rate ◽  
Temperature Lapse Rate ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Ice Particles ◽  
The Pacific ◽  
The Impact

Abstract. Gravity waves are an ubiquitous feature of the atmosphere and influence clouds in multiple ways. Regarding cirrus clouds, many studies have emphasized the impact of wave-induced temperature fluctuations on the nucleation of ice crystals. This paper investigates the impact of the waves on the motion and distribution of ice particles, using the idealized 2-D framework of a monochromatic gravity wave. Contrary to previous studies, special attention is given to the impact of the wind field induced by the wave. Assuming no feedback of the ice on the water vapor content, theoretical and numerical analyses both show the existence of a wave-driven localization of ice crystals, where some ice particles remain confined in a specific phase of the wave. The precise location where the confinement occurs depends on the background relative humidity, but it is always characterized by a relative humidity near saturation and a positive vertical wind anomaly. Hence, the wave has an impact on the mean motion of the crystals and may reduce dehydration in cirrus by slowing down the sedimentation of the ice particles. The results also provide a new insight into the relation between relative humidity and ice crystals' presence. The wave-driven localization is consistent with temperature–cirrus relationships recently observed in the tropical tropopause layer (TTL) over the Pacific during the Airborne Tropical Tropopause EXperiment (ATTREX). It is argued that this effect may explain such observations. Finally, the impact of the described interaction on TTL cirrus dehydration efficiency is quantified using ATTREX observations of clouds and temperature lapse rate.

scholarly journals Cirrus and water vapour transport in the tropical tropopause layer – Part 2: Roles of ice nucleation and sedimentation, cloud dynamics, and moisture conditions

2014 ◽  
Vol 14 (22) ◽  
pp. 12225-12236 ◽  
Author(s):  
T. Dinh ◽  
S. Fueglistaler ◽  
D. Durran ◽  
T. Ackerman
Keyword(s):  
Water Vapour ◽  
Initial Conditions ◽  
Ice Nucleation ◽  
Radiative Heating ◽  
Radiative Effects ◽  
Downward Flux ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Instantaneous Removal ◽  
Moisture Redistribution

Abstract. A high-resolution, two-dimensional numerical model is used to study the moisture redistribution following homogeneous ice nucleation induced by Kelvin waves in the tropical tropopause layer (TTL). We compare results for dry/moist initial conditions and three levels of complexity for the representation of cloud processes: complete microphysics and cloud radiative effects, likewise but without radiative effects, and instantaneous removal of moisture in excess of saturation upon nucleation. Cloud evolution and moisture redistribution are found to be sensitive to initial conditions and cloud processes. Ice sedimentation leads to a downward flux of water, whereas the cloud radiative heating induces upward advection of the cloudy air. The latter results in an upward (downward) flux of water vapour if the cloudy air is moister (drier) than the environment, which is typically when the environment is subsaturated (supersaturated). Only a fraction (~25% or less) of the cloud experiences nucleation. Post-nucleation processes (ice depositional growth, sedimentation, and sublimation) are important to cloud morphology, and both dehydrated and hydrated layers may be indicators of TTL cirrus occurrence. The calculation with instantaneous removal of moisture not only misses the hydration but also underestimates dehydration due to (i) nucleation before reaching the minimum saturation mixing ratio, and (ii) lack of moisture removal from sedimenting ice particles below the nucleation level. The sensitivity to initial conditions and cloud processes suggests that it is difficult to reach generic, quantitative estimates of cloud-induced moisture redistribution on the basis of case-by-case calculations.

scholarly journals Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration

2004 ◽  
Vol 4 (6) ◽  
pp. 7433-7462
Author(s):  
E. Jensen ◽  
J. B. Smith ◽  
L. Pfister ◽  
J. V. Pitman ◽  
E. M. Weinstock ◽  
...  
Keyword(s):  
Water Saturation ◽  
Accommodation Coefficient ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
High Threshold ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Accommodation Coefficients ◽  
The Tropics

Abstract. Recent in situ measurements at tropical tropopause temperatures as low as 187 K indicate supersaturations with respect to ice exceeding 100% with little or no ice present. In contrast, models used to simulate cloud formation near the tropopause assume a supersaturation threshold for ice nucleation of about 65% based on laboratory measurements of sulfate aerosol freezing. The high supersaturations reported here, along with cloud simulations assuming a plausible range of temperature histories in the sampled air mass, indicate that the vast majority of aerosols in the air sampled on this flight must have had supersaturation thresholds for ice nucleation exceeding 100% (i.e. near liquid water saturation at these temperatures). Possible explanations for this high threshold are that (1) the expressions used for calculating vapor pressure over supercooled water at low temperatures give values at least 20% too low, (2) most of the available aerosols had a composition that makes them much more resistant to ice nucleation than aerosols used in laboratory experiments, and (3) organic films on the aerosol surfaces reduce their accommodation coefficient for uptake of water, resulting in aerosols with more concentrated solutions when moderate-rapid cooling occurs and correspondingly inhibited homogeneous freezing. Simulations of in situ cloud formation in the tropical tropopause layer (TTL) throughout the tropics indicate that if these decreased accommodation coefficients and resulting high thresholds for ice nucleation prevailed throughout the tropics, then the calculated occurrence frequency and areal coverage of TTL cirrus would be significantly suppressed. However, the simulations also show that even if in situ TTL cirrus form only over a very small fraction of the tropics in the western Pacific, enough air passes through them due to rapid horizontal transport such that they can still effectively freeze-dry air entering the stratosphere.

Sign in / Sign up

Export Citation Format

Share Document